1. Field of the Invention
The invention relates to a gate reader that reads information from a wireless tag, in particular, a gate reading antenna.
2. Description of the Related Art
A technology of a wireless tag as an automatic recognition technology is superior to a popular bar-code system in that non-contact and long distance reading can be realized. As a product that makes use of the long distance readability, an antitheft wireless tag gate reader (hereinafter, referred to as a gate reader) is well known. The gate reader is a device that communicates with a wireless tag attached to a passenger or an article that goes through the gate reader to read information in the wireless tag. An existing gate reader, as shown typically in FIG. 1, reads information recorded in a wireless tag that goes through between reader antennas 61 disposed facing each other. In the case of the reader antennas 61, antennas are mounted in three stages in an up and down direction.
A wireless tag 72, as shown in FIG. 2, is constituted including an IC chip 71 and a tag antenna 73 connected thereto. A communication time during which an existing gate reader reads information in the wireless tag 72, depending on a communication procedure and an amount of data, takes at least several milliseconds to several tens milliseconds. A recognition target (not shown in the drawing) that is a person or an article with the wireless tag 72 attached thereto has to stay in or go through a read zone at least during the read time. Accordingly, when a transit speed (walking speed, transportation speed) is high, a sufficient read time cannot be secured, resulting in incapability of reading.
When a transit speed is too high to be sufficient in the read time, generally, as shown in FIG. 3, a plurality of antennas 81a, 81b and 81c is arranged in a transit direction to lengthen a communication zone. However, in this case, the gate reader 81 becomes very large. As a method of solving this, Japanese Patent Publication No. 2002-271229 for instance discloses that the directivity of an antenna is altered. In this method, the directivity of an antenna can be varied mechanically or electrically to narrow a read zone of the antenna. However, it is intended to narrow a read zone of the antenna but not to expand the read zone and to miniaturize a device size.